Process for producing an insulating coating on articles containing aluminum



E. w. KUTTNER PROCESS FOR PRODUCING AN INSULATING COATING ON ARTICLES CONTAINING ALUMINUM April 12, 1932.

Filed March 15, 1928 Patented Apr. 12, 1932 UNIT-ED STA ERNST WOLFGANG KU'I'TNER, F BERLIN, GERMANY -PBOCESS FOR PRODUOIN G AN INSULATING COATING on narrates conramme ALUMINUM Application filed larch 15, 1928, Serial No. 261,750, and in Germany Illl'arch 22, 1927.

It is generally known that aluminum and 4 aluminum-alloys are coated, when exposed to the air, with a thin oxide layer which, for certain purposes, is sufficient as electric insu- 5 lation. For other purposes the thin oxide coating produced in this manner is however,

not su cient as insulation, and in such cases it is necessary to provide a thicker insulating layer on the aluminum or aluminum alloys. This is done, in a manner known per se, by producing either by electrolytic process or by the action of suitable chemical fluids solidly adhering coatings'or precipitates of aluminum oxide or other aluminum combinations on the metallic surfaces. It is for instance possible to produce the insulatin layer on the metallic surface by treating t e article with oxidizing liquids, gases or vapours. The aluminum or the like might further eventually be provided with covers of another type having an insulating effect. I

In the use of such covers and coatings exists however under certain conditions a diflicultly in sofar, as the insulating covers of aluminum oxide or the like produced in this manner are brittle, and break or peel consequently easia -ly when flexible articles, as wires, bands, thin plates and the like having these covers, are

being bent; or the brittle coatings might even cause the breaking of thin wires, bands or sheet metal plates.

- It has been found that this inconvenience can be avoidedby submitting the articles to be fitted with the insulating covers to a mechani-v cal treatment while they are being treat-ed with the fluid (liquids, gases or the like) designed to produce the coatin or precipitate. This mechanical treatment e ects a kneading of the coating during its formationand can consist for instance in continuous or intermittent hammering, beatin rubbing or .to and fro bendingof the flexi le metal articles in such a manner, that the insulating cover forming on the same is produced during this treatment. This cover has thcn'the desired elasticity and will neither break nor peel at the bending of the metal articles. The cover which has been formed can serve, owing to its elasticity and great resisting capability, with advantage also as protecting layer against other influences than electric, commg from the outer side.

he new processmay be carried out in a slmple manner, for instance in that the wires or bands of aluminum or aluminum alloys, which for example are treated as anode in an electrolytic bath, are guided through the bath over plns or rollers arranged alternately in dlfierent positions, so that the wire or the band conducted over the same adopts a serpentine or zig-zag shape. lThe wire or the band is therefore, when passing through the electrolytic bath,'alternately bent to and fro and thus submitted to the mechanical knead-- mg treatment during the formation of the oxide layer and in accordance with the present invention. For the electrolytic bath,

bases or solutions of salts can be used, which have an oxidizing'eifect; solutions of organic acids as oxalic and or thel ke or inorganic acids as chromic acid or nitric acid are preferably used as bath-liquid. In a quite simllar manner the mechanical treatment can be carried out also when the formation of the oxide layer or the like has to be produced by the action of gases or vapours on the metallic. surfaces Other means for bending to and fro and for other mechanical treatment of the wires, bands and sheet metal plates during, the formation of the insulating layer may evidently be used also.

When the process is carried out in such a manner that thewire or the like is conducted in the medium producing the coating over rotatably mounted rollers, the arrangementv may be made so that a rotatably mounted body of regular or irregular shape, having a spiral groove, serves as guiding for the wire or the like so that on one and the same roller several different bendings are given to one wire. The arrangement is preferably made so that several rollers are provided, and the wire is conducted several times around the same. The desired toand fro-bending is specially favoured when at least one of the rollers rotates in a direction opposite to the direction of rotation of the other rollers.

This might be obtained for example by juxtaposing an odd number of rollers over which the wire or the like is conducted in serpentine the coating is obtained, as the bending of the same is carried out alternately in opposite directions. The rollers or cylinders may further have a roughened, irregular or undulated surface, for instance teeth, so that the 1 wire 'or the like is not only bent several times but also submitted on the surface to a mechanical treatment.

The continual bending of thick wires requires much power and causes a strong fric- .t1on on the rollers and in the roller bearings.

The same is the case for thin wires, when a greater number of bending points of rollers are provided. When therefore metals are to be treated which possess only a low tensile resistance or a considerable (dilatation or expansion, it is advisable to reduce the tensile stress as much as possible and to drive at least some of the guide rollers with that speed at which .the wire or the like has to be conducted wire its through the oxidizing medium. In certain cases all -guide rollers for the wire and this e f may be conducted at similar speed, i. e. driven from one single outer driving mechanism, whereby a complete relieving of tension is obtained for the wire or the like.

v V The guide rollers or their driving means may be preferably arranged on one or several movable supports to be inserted into the bath or the like in order to save room and to facilitate attendance. The arrangement may be further made, that several wires or bands are simultaneously treated in the same bath.

An embodiment of an apparatus for carrying out the invention is diagrammatically illustrated in the accompanylng drawings, and by way of example an electrolytic oxidation-apparatus with continuous current is selected. The apparatus may however work with alternating current.

Fi 1 shows the bath with the apparatus and t e means for feeding and delivering the wire.

Fig. 2 shows the supporting frame carry-* ing the bending device and the driving means.

The wire or metal band 1 to be oxidized or coated is supplied from the left over tensioningand guiding-rollers 6 and 7 into the bath 3 and delivered from the bath over pulleys 2 to the winding-up device. The metalrollers or ulleys 6 are mounted on an electricity con ucting plate 5 or the like, which forms the one pole and at continuous current the positive electrode, so that the bare wire becomes positive by touching this current supply. .In the bath 3 plates 4 or the like are immersed which are connected to the other pole of the source of current. The bending to and fro of the wire 1 takes lace, accordmg to the invention, on-two dis s or rollers 13,

15 rotatably mounted in a supportin frame 8. Each roller 13, 15 has severa guide grooves 14, 16 respectively, so that the wire is wound several times around the rollers and conducted in these guide grooves. The

with several parallel annular grooves, a nuin 'ber of rollers might be used havin each only one guide groove and the indivi ual rollers may be mutually movable in a certain llmit.

.The wire is conducted so that it crosses'between the two rollers 13 and 15, the bending direction of the wire being reversed each time at the transition from one roller to the other. In order to relieve the wire of the tension as much as possible, the roller 13 is driven from the outer side. With this object in view a driving pulley 9 is mounted on the frame 8, which carries the rollers 13 and 15, on'the outerside of the same, and connected by a chain or rope drive 10, 11 to the axle of the roller 13, said pulley 9 being driven in a suitable manner, for instance from a motor. Other guide rollers, for instance those 15, 6, 7, or 2, may also be driven in a similar man ner. The reel or winding up device for the finished wire and eventually also the drum "from which the bare wire comes, may be driven at the same speed so that the wire is relieved of any tension, even when it is bent to and froin a great number of windings. Instead of arranging the guide rollers 13, 15 as shown the one above the other in an upright frame 8 on horizontal axles, a horizontalframe may be used in which the rollers/are journalled the one at the side of the other on vertical axles. I The upright or vertical frame has the advantage that the points at.

which the wire to be treated enters into and comes out from the bath are situated in the surface of the bath. Several wires may be located at the same time in the same bath, when several bending and guiding devices are arranged, which may all be driven from the same point.

Having now particularly described and ascertained the nature ofmy said invention, I declare that what I claim is:

1. The method of subjecting flexible articles of metal containing aluminum to a treatment with an oxidizing agent and simultaneously to a kneading process until the oxide coating formed is rendered flexible.

2. Method to provide on flexible articles of metal containing aluminum'a solidly adhering elastic cover, consisting in that the articles are treated with a fluid designed to produce a coatin layer on the surface of the articles and are nt to and fro during the treatpressing, rubbing and 'kne'adingthe entire cles are treated with a fluid designed to proment with the fluid-simultaneously. oomsurface of the saidlayer until the coating layer is rendered flexible.

3. Method to provide on flexible articles" of metal containing aluminum a solidly adhering elastic cover, consisting in that the articles are treated with the'fluid designed to produce a coating layeron the surface of the articles and are conducted over rotatable rollers adapted to bend the articles alternately to and fro in the medium producing the coating and simultaneously knead the entire surface of the coating layer.

4. Method to provide on flexible articles of metal containing aluminum a solidly adhering elastic cover, consisting in that the artiduce a coating layeron the surface of the articles and are conducted over rotatable rollers adapted to bend the articles alternately to and fro in the medium producing the coating and tot-horou hly knead the entire surface of the coating ormed, at least one of the said rollers being positively driven.

5. A process of improving coverings of aluminum oxide formed on the surface of a metallic article which contains aluminum consisting in subjectingthe article during the formation of the said covering to a mechanical treatment by which its entire surface undergoes tensile and compressive stresses.

6. Method to provide on flexible articles of metal containing aluminum a solidly adhering elastic cover, consisting in thatthe articles are treated with a fluid designed to produce a coating layer on the surface of the articles and said coating layer is submitted during its formation to a mechanical treatment, adapted to thoroughly compress and rub said layer until it is rendered flexible.

In testimony whereof I have hereunto set my hand,

. ERNST WOLFGANG KUTTNER, 

